Riverine and early ocean migration and mortality patterns of juvenile steelhead trout (Oncorhynchus mykiss) from the Cheakamus River, British Columbia

Abstract

High mortality (65–73%) occurred in the first month of the smolt migration in a population of wild steelhead trout. We used acoustic telemetry to monitor the downstream, estuarine, and early ocean migration of tagged smolts and estimate their mortality rates. After entering the Strait of Georgia most smolts migrated north through Johnstone and Queen Charlotte Straits rather than south through the Strait of Juan de Fuca. Of 51 smolts tagged in 2004 (49 in 2005), 36–38 (41–42) survived to leave freshwater and 14–19 (13–14) survived to leave the Strait of Georgia system. Mortality rates in separate segments of the migration were correlated with segment distances. An additional component of mobile sampling showed that few smolts died during the migration through Howe Sound. Migration rates averaged 0.7–0.9 body lengths per second (BL s−1) downstream and 1.0–2.6 BL s−1 in ocean waters. Aggregated detection probabilities of 92–96% on lines of ocean receivers suggest that migration routes of small fishes can be quantified over several hundred kilometres, and survival rates can be estimated for even a modest number of tagged fish. Quantifying mortality patterns during the smolt migration could help to determine causes of low marine survival rates observed in recent years.

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Acknowledgements

We are grateful to Melinda Jacobs, Erin Rechisky, Adrian Ladouceur, Jayson Semmens, Paul Winchell, Heidi Lydersen, Scott Lincez, Orie McKenzie, Valeria Vergara, Pablo Trujillo, Dave Preikshot, Valerie Caron, Ross Thompson, Peter Rossing, David Thomson, Sherman Lai, David O’Brien, Ian Hatton, Line Christensen, Steve Martell, Dawit Tesfamichael, Pi Liu, Natalie Ban, Jonathan Anticamara, Doug Sandilands, Dal, Nathan Taylor, Brian Starzomski, Jordan Rosenfeld and Caroline Melville for their willing assistance in the field. We thank Martin Castonguay, Gilles Lacroix, and Derek Knox of Fisheries and Oceans Canada as well as Fred Goetz from the U.S. Army Corps of Engineers for generously lending acoustic telemetry equipment. We thank Sonia Batten and Isabelle Gaboury for data management help and all POST members for support. We thank Eric Taylor and two anonymous reviewers for helpful comments on the manuscript. Permission for surgical implant of tags into smolts was granted by the Department of Fisheries and Oceans Animal Care Committee. Funding was provided by the Fish America Foundation (American Sportfishing Association), the Pacific Salmon Foundation, the Gordon and Betty Moore Foundation, the Alfred P. Sloan Foundation (Census of Marine Life), and through a graduate scholarship from the National Science and Engineering Research Council of Canada to MM.